We examine the radiation shielding requirements for protecting the inhabitants of orbital space settlements. Following an extensive analysis of the literature, we recommend a limit of 20 mSv/yr for the general population and 6.6 mGy/yr for pregnant women based on the most relevant standards, existing data and background radiation on Earth. In a surprising result, radiation measurements on the International Space Station (ISS) and our calculations using OLTARIS, NASA’s online radiation computational tool, indicate that space settlements in Equatorial Low Earth Orbit (ELEO) below about 500 km are likely to meet this standard with little or no dedicated radiation shielding. This reduces the mass of typical orbital space settlement designs by 95% or more, suggesting that the easiest place to build the first space settlements is in ELEO due to proximity to Earth and relatively low system mass.

It is important to note that there are significant uncertainties in our understanding of the human effects of the continuous low-level high-energy particle radiation characteristic of space in general and ELEO in particular that need to be resolved. Thus, our conclusions should be considered preliminary.

Abstract. The geomagnetic field seems to be collapsing. This has happened many times in the deep past, but never since civilization began. One implication is that the cost of space settlement will increase substantially if we do not expedite deployment of initial facilities in low Earth orbit. Another implication, less certain but much more damaging, is that the collapse may lead to catastrophic global cooling before the end of this century. We must establish self-sufficient communities off Earth before that happens.

An enormously successful first annual Space Settlement Summit hosted by the National Space Society (NSS) occurred on January 10-11, 2017, in Santa Monica, California. Industry leaders, financial experts, scientists and engineers, and leading space activists were brought together to assess the state of the art driving space settlement.

“The resources of Earth are limited and humanity is increasingly constrained by these limits. This is particularly true when reasonable environmental considerations are taken into account” said Mark Hopkins, Chair of the NSS Executive Committee. “Fortunately, the vast majority of the resources of the solar system both in terms of energy and materials lie in space rather than on Earth. Space settlement allows us to tap into these resources, thus smashing the resource constraints of Earth. Space settlement can create a hopeful prosperous future for all of humanity.”

“With Elon Musk calling for the colonization of Mars, and Jeff Bezos looking forward to millions of people living and working in space, space settlement is an idea whose time has come,” said Dale Skran, NSS Executive Vice President.

“NSS has been developing a Roadmap for space settlement for a number of years (see www.nss.org/settlement/roadmap)” added Bruce Pittman, NSS Senior Vice President and Senior Operating Officer. “The Space Settlement Summit will provide input that guides NSS’s current updating of the Roadmap. Anyone interested in learning more about how NSS is supporting space development and settlement should attend the International Space Development Conference in St. Louis, Missouri, May 25-29 (isdc2017.nss.org).”

The author compiled every known orbital space settlement design into a database. Grouped into chronological ‘eras,’ the database describes basic information for each design: population capacity, dimensions, gravity level, energy source, etc. Using this information one can conclude that interest in space settlement is increasing, 1g is the preferred gravity level, solar power is the preferred energy source, and a torus is the preferred geometry. As for location, Earth-Moon Lagrange points dominate but there is a budding movement to place settlements in low Earth orbits. The database is accessible at www.nss.org/settlement/journal/Space-Settlement-Designs-Database-12.19.16.pdf.

Very smart and capable people have been dreaming about space settlement for decades, but these dreams have not come to fruition. Why? Because building space settlements is extraordinarily difficult. There are two ways to overcome this: a lot of money or an easier way. An enormous pile of government money doesn’t seem to be headed our way, but it turns out there is a much easier way.

The location of the usual space settlement suspects includes the Moon, Mars, asteroids, and the Earth-Moon L5 point (or other high Earth orbit). They all suffer from one very serious problem: they are very far away, anywhere from 363,000 to 400,000,000 km from Earth. This makes everything we want to do extremely difficult.

All space settlements need pressurized habitat, power systems, thermal control, communications, life support, materials recycling, and radiation shielding. As radiation levels in space are high compared with Earth, the mass of the radiation shielding completely dominates the mass of most space settlement designs because inadequate shielding can lead to cancer, cataracts, and sterility. In orbits beyond Earth’s magnetic field, radiation protection requires about seven tons of water, or eleven tons of lunar regolith, per square meter of hull and a little bit less on the surface of Mars or the Moon. This amounts to millions of tons of material for a settlement big enough that people might actually enjoy living in it once the excitement of moving to space wears off, perhaps 100 m across at least. If the radiation shielding was not needed space settlement would be vastly easier. [See “Orbital Space Settlement Radiation Shielding,” Al Globus and Joe Strout, preprint, June 2016, which contains data and references for radiation related claims in this article.]

Figure 1. Radiation measurements taken on the ISS (International Space Station). Note the very low levels (blue) near the equator, which is on the horizontal line starting at 0 on Latitude scale. Image credit NASA.

It is our incredibly good luck that there is a region of space, very close to Earth, where radiation levels are much, much lower than at the usual suspects. This is Low Earth Orbit (LEO) directly over the equator (or ELEO)—see figure 1. The Earth’s magnetic field protects this region from all but a small fraction of space radiation, albeit the most energetic part. Radiation levels are so low that below about 500 km it is possible, even likely, that no dedicated radiation shielding will be necessary. This means that a 100 m diameter cylindrical settlement in ELEO might have a mass of around 8.5 kTons, hundreds of times less than above the Earth’s magnetic field. [See “Space Settlement: an Easier Way,” by Al Globus, Stephen Covey, and Daniel Faber, June 2016, which contains data and references for settlement related claims in this article.] This entire mass could be launch by about 160 Falcon Heavy launches. This is not for a few capsules connected by tunnels, but an open living area comparable in size to a large cruise ship with zero-g recreation at the axis of rotation, full 1-g pseudogravity just inside the hull, and recreational space walks.

If you are familiar with free space settlement issues you might object that to get Earth-normal pseudogravity with a 100 m diameter you need to rotate a settlement at about four rpm (revolutions per minute), which will make many people sick. That is true, but it is also true that people adapt to rotation at four rpm within a few hours or days and are subsequently just fine. If you were to move to Nepal you would be altitude sick for a few days, but Nepal is still a beautiful place to live. [See “Space Settlement Population Rotation Tolerance,” Al Globus and Theodore Hall, preprint, June 2015, which contains data and references for human response to rotation claims in this article.]

You might also note that most Mars/Lunar settlement schemes involve putting a module on the Martian/Lunar surface with far less than 160 launches. But that’s for a module a few meters across, similar to vehicles that have been in LEO off and on since the 1960s and much smaller than the ISS which has been continuously inhabited since 2000. For a given size, the total mass of the material needed from Earth for early ELEO vs Mars/Lunar settlements is about the same. Low radiation levels in ELEO mean settlements there require little or no radiation shielding. Although radiation levels on the Martian/Lunar surface are high, about half that in free-space, local materials can be used for radiation shielding. However, Mars/Lunar residents will rarely leave their habitat due to the radiation and LEO development will continue to be far ahead because LEO is at least 100,000 times closer than Mars and 720 times closer than the Moon giving ELEO a massive logistical advantage.

While space settlement may be vastly easier to get started in ELEO than anywhere else, it is still a massive task. Launch vehicle prices need to come down by a factor of perhaps 50, reliable nearly-closed large-scale life support must be developed, and a million engineering problems must be solved so that people can live comfortably, safely, and enjoyably in space. Absent a gigantic pile of government money, how can this been done? One word: tourism.

Tourism can supply the two things essential to market-driven equatorial LEO settlement development:

A very high flight rate to make fully reusable launchers economically viable. We estimate at least > 10,000 flights per year is needed, compared to < 100 today.

A market for ever larger and more sophisticated space hotels starting with the ISS.

Seven paying tourists have flown to the ISS (one twice) on a 7-10 day trip, but right now no seats are for sale. Rumor has it that the first few space tourists paid about $20 million and the most recent flight was on the market for $50 million. While this is discouraging (the price is absurdly high and headed in the wrong direction) surveys suggest that if someone could drop the price a bit, much larger numbers of people would want to go.

The good news is that the best advertised price to fly to LEO so far is $26.25 million, although the vehicle is still in development. If this is successful and makes a profit, as more flights are booked economies of scale can reduce the price, which in turn increases the size of the market, which enables a reduction in price, which increases the size of the market … and so on. We need to get on this virtuous spiral of dropping costs leading to bigger markets leading to lower cost. If the cost is low enough the market is measured in millions of customers per year, which is the sort of market needed for the kind of low-cost high-flight-rate transportation system necessary to settle space regardless of destination.

All those tourists need somewhere to go, meaning we will need space hotels. The first ones may be small to keep up-front costs down but if space tourism is successful the desire for bigger, more sophisticated, and more comfortable hotels could drive constant improvement.

As luck would have it, most of what is needed for ELEO settlements is also important for hotels: recycled air, water, and food, power systems, communications with Earth, etc. Hotels may even want artificial gravity, achieved by rotation, so that guests need not learn how to use a 0-g toilet—which is difficult and, when you screw up, disgusting as everything floats around and gets into places you would rather it not. Also, staff can have longer tours of duty, reducing transportation costs, as their bodies will not be continuously subject to weightlessness, which can cause a number of problems. Once hotels have developed most of the necessary technology and supporting infrastructure, building the first space settlement should be not much more difficult than building another hotel.

In an internet survey of space enthusiasts, 30% of respondents said they would very much like to live in Kalpana Two in ELEO, including raising their children, and are willing to spend 75% of their wealth and lifetime income to do so. That’s enough to get space settlement started.

Although building Kalpana Two after a few decades of space tourism development may be much easier than starting from scratch, it is still a monumental effort requiring a great deal of money and those funds will be easier to raise if Kaplana Two and later settlements have a mass-market product to sell to Earth.

Kalpana Two residents could assemble and test extremely large communication satellites, much larger than those launched today. Large comsats are attractive because the larger the spacecraft antenna and the larger the power-producing solar arrays the smaller the antenna on the ground must be and the less battery power is needed, two things for which there is a large and growing market. ELEO is also a good place to manufacture ultra-light solar sails, as the sails need not be folded into a fairing, launched and unfolded. While the market for solar sails is small, if you cover one side of the sail with power-producing electronics you have extremely light power arrays which can be used for large comsats. Put fiber lasers on the other side of the sail and you can beam power, first for in-space applications, such as power for Kalpana Two, and later to deliver power to Earth—a gigantic market. [See “Towards an Early Profitable PowerSat,” Al Globus, Space Manufacturing 14: Critical Technologies for Space Settlement, NASA Ames Research Center, Mountain View, CA, October 29-31, 2010, and “Towards an Early Profitable PowerSat, Part II,” Al Globus, Ion Bararu, and Mihai Radu Popescu, International Space Development Conference 2011, National Space Society, Huntsville, Alabama, 1822 May, 2011.]

The first equatorial LEO settlement is the hardest to build. The second and subsequent ones will be easier because lessons will be learned and infrastructure developed. We estimate there is room for at least a few million people spread out in a few hundred settlements in equatorial LEO. This can provide the key requirement for commercially viable lunar and asteroid mining: a decent sized market in space. It is hard for extraterrestrial materials to compete on Earth due to transportation costs. However, in space lunar and asteroidal materials have the edge due to high launch costs from Earth. The problem today is that the in-space market is a single satellite designed for in-space refurbishment (the Hubble Space Telescope) and six people on the ISS, which is tiny. Equatorial LEO settlement is a game changer for lunar and asteroidal mining.

Once the mining infrastructure to deliver substantial materials to equatorial LEO is in operation and ELEO fills up with settlements, it will be time for the next step: settlements in orbit beyond the Earth’s protective magnetic field. These settlements will require millions of tons of radiation shielding, which can provide a market for a huge expansion of lunar and asteroidal mining. This, in turn, can provide economic support for mining settlements on the Moon and co-orbiting with asteroids. This network of settlements can then expand to Mars and the asteroid belt. Of course, for Mars and the Moon the problems associated with raising children in partial-g including but not limited to growing up with weak muscles and bones will have to be addressed.

At this point we will be well on our way to turning the resources of this solar system into living, breathing settlements in huge numbers. The next step, of course, is to send groups of settlements to Alpha Proxima and start the billion-year project of greening our galaxy. After all, if you have lived for 50 generations in orbital space settlements does it matter much if you are close to Sol or on the way to the nearest star? Probably not, at least for some, but that is a task for future generations. Our mission, should we decide to accept it, is to get space tourism on track to develop the technology and infrastructure necessary to build Kalpana Two in equatorial LEO. This tape will not self-destruct.

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Al Globus is a member of the National Space Society Board of Directors.

At today’s meeting of the International Astronautical Congress (IAC) in Guadalajara, Mexico, Elon Musk, CEO of Space X, announced his bold plan to build a city on Mars. For over 40 years the National Space Society has led advocacy for space settlement. According to Mark Hopkins, economist and Chair of the Executive Committee of the National Space Society, “The vast majority of the resources of our solar system lie in space rather than on the Earth. By settling Mars and other locations in space we can overcome the resource limits of Earth leading to a hopeful, prosperous future for all of humanity.”

During the talk Musk detailed the Interplanetary Transport System (ITS) for the first time. The first stage of the ITS towers 77.5 meters with a diameter of 12 meters and uses 42 Raptor engines to provide a total of 28 million lbs of thrust. The second stage is 49.5 meters long, 17 m in diameter, uses 9 Raptor engines, and comes in both a crew/cargo model and a tanker model. Musk’s plans are based on four key approaches: full reusability of all components, refueling in orbit around Earth, refueling on Mars with locally produced propellant, and using a rocket fuel (methane/oxygen) that can be easily manufactured on Mars. Musk envisions that the eventual cost of a ticket to Mars will be in the $100K-$200K U.S. dollars range, allowing ordinary people to eventually travel to Mars.

SpacX ITS launchSpaceX ITS reusable first stage returnSpaceX ITS refueling in orbitSpaceX ITS approaching MarsSpaceX ITS final approach to MarsSpaceX ITS Mars entrySpaceX Raptor engine testSpaceX has already built a prototype ITS composite fuel tank

What has been a bold vision of the future for humanity is now becoming reality. Humanity has begun the first concrete steps towards space settlement. The next decade will be one of the most pivotal in human history. Today we are beginning the journey to becoming a multiplanetary species.

In recognition of these momentous developments taking place the National Space Society is convening the first “Space Settlement Summit” in January to bring together leading people, companies and organizations that are making space settlement a reality. Participation in this event will be by invitation only and limited to entrepreneurs, scientists, engineers, venture capitalists, and thought leaders deeply involved in making space settlement a reality. The objective of the event will be to show the synergistic in-space ecosystem that is emerging; to facilitate a convergence of interests and opportunities among the key players; and to identify critical issues along the path to space settlement. We are at the dawn of a new era for humanity and the National Space Society is continuing its role as the leading voice for space settlement.

Musk’s reveal of his Mars colonization plan follows the announcement September 12th of the Blue Origin “New Glenn” heavy-lift vehicle by Jeff Bezos. The New Glenn is 7 meters in diameter and comes in both a two stage and a three stage version. The reusable first stage is powered by seven BE-4 engines fueled by liquid natural gas and liquid oxygen, providing 3.85 million pounds of thrust. The second stage uses a single BE-4 engine, and the optional third stage a single liquid hydrogen-oxygen BE-3 engine, the same engine used in the flight proven reusable New Shepard sub-orbital vehicle.

“The New Glenn is a major step forward for commercial space,” said Dale Skran, NSS Executive Vice President. “With the SpaceX ITS and Falcon Heavy, the United Launch Alliance Vulcan, and the Blue Origin New Glenn operational, the U.S. will have four domestic options for commercial medium to heavy lift. This will allow NASA to make use of commercial heavy lift services with greater confidence than if only a single operator existed.”

The U.S National Space Policy of 2010 states “To promote a robust domestic commercial space industry, departments and agencies shall: Purchase and use commercial space capabilities and services to the maximum practical extent when such capabilities and services are available in the marketplace and meet United States Government requirements.”

“NASA ought to welcome the usage of the ITS, Vulcan, the New Glenn and the Falcon Heavy in future NASA planning,” said Skran. “NASA can only benefit from the existence of multiple commercial medium to heavy lift providers with re-usable first stages that offer the possibility of significant cost reductions.”

Milestone 2 on the NSS Space Settlement Roadmap is titled “Higher Commercial Launch Rates and Lower Cost to Orbit” (http://www.nss.org/settlement/roadmap/RoadmapPart2.html). Future NASA usage of commercially available partially or fully re-usable medium to heavy lift vehicles will be critical to achieving this milestone.

“Competition like that seen between Blue Origin and SpaceX is key to rapid progress in space,” said Bruce Pittman, NSS Senior Vice President. “Elon just presented a plan for settling the solar system in this century that is realistic and affordable. In my paper, ‘A Pathway to a Thriving Commercial Space Economy’ at IAC, I also laid out a path forward to a thriving new economy in space that produces new opportunities for all.”

NSS has been pushing hard via legislative outreach in cooperation with the Alliance for Space Development to make space development and settlement part of the objectives that guide NASA. In March 2016 Rep. Dana Rohrabacher introduced H.R.4752 the “Space Exploration, Development, and Settlement Act (see https://www.congress.gov/bill/114th-congress/house-bill/4752/text) to make development and settlement of space part of the fundamental law governing NASA.

More recently, on September 21, 2016, the Senate Commerce, Science, and Transportation Committee marked up S.3346, the NASA Transition Act of 2016. This bi-partisan Bill, co-sponsored by Senators Cruz, Nelson, Rubio, Peters, Wicker, and Udall, contains the following ground-breaking statement:

Section 202(a) of the National Aeronautics and Space Administration Authorization Act of 2010 (42 U.S.C. 18312(a)) is amended to read as follows:
“(a) LONG-TERM GOALS—The long-term goals of the human space flight and exploration efforts of NASA shall be—
“(1) to expand permanent human presence beyond low-Earth orbit and to do so, where practical, in a manner involving international, academic, and industry partners; and
“(2) the peaceful settlement of a location in space or on another celestial body and a thriving space economy in the 21st century.”

On Tuesday September 27, on the second day of the International Astronautical Congress (IAC) in Guadalajara, Mexico, Elon Musk will deliver a special keynote presentation on “Making Humans a Multiplanetary Species.”

Musk will discuss the long-term technical challenges that need to be solved to support the creation of a permanent, self-sustaining human presence on Mars. The technical presentation will focus on potential architectures for colonizing the Red Planet that industry, government and the scientific community can collaborate on in the years ahead.

Here’s a virtual space settlement “ball drop” experiment courtesy of Joe Strout. The ball starts out six meters above the deck, initially stationary with respect to the rotating settlement. Then it is dropped, much like Galileo dropping stones from the Leaning Tower of Pisa, but it results in a behavior that Galileo never saw:

The viewpoint is lined up for optimally seeing the slight pull to the left. In reality, of course, there is no pull to the left… the ball is traveling in a straight line, at a constant velocity from the moment it was released, and the settlement is rotating around it. Note that the appearance of moving toward the viewer is an illusion: the ball is not being dropped from the vertical dark pillar but from an invisible platform the same distance toward the viewer as where the ball lands.

Details for the curious: The deck here has a 224-m radius and spins at 2 RPM, simulating 1G. The white ceiling at the top of the view is about 130 m up. Those deck plates are 2 m squares, though unfortunately they don’t line up perfectly with the ball’s starting position — but if you can detect a slight bend in the plating, that does align with where the ball starts. So the ball’s apparent sideways motion is about a meter or so, over a 6 meter drop.

Note that this simulation assumes there is no air here; the ball is falling as in a vacuum. In a real settlement, of course, air would apply a force in the direction of the settlement’s spin, reducing this Coriolis effect by some amount that depends on the aerodynamics of the object.

Abstract: The cost of rocketing cargo into space is very high. Great savings can result if local resources like oxygen and materials from lunar regolith are used to build and expand Moon bases and create industrial settlements to supply materials for solar power satellites and space settlements, tourism, planetary defense, asteroid mining and research stations. This paper attempts to illustrate the components of a lunar “industrial seed” consisting of equipment needed to produce materials on the Moon and establish a growing industrial presence there that leads to space settlement. The first section discusses some of the issues surrounding transportation to the Moon and the second section quickly examines materials production, manufacturing and construction. Space settlers and industrialists must get an idea of how much propellant and cargo must be launched from Earth and plan out the actual cargoes to determine the size of capital outlay for a Moon mining project.